The block copolymer has a molecular structure in which polymer blocks each with a distinct chemical structure are connected to one another by covalent bonds. The block copolymer can be constructed in a structure such as a sphere, a cylinder and a lamella through phase separation. The structure that is formed as the result of the self-assembly phenomenon of a block copolymer has a domain whose size can be adjusted over a wide range, and it can be constructed in various forms which can be applied to the production of a variety of next-generation nanodevices, magnetic storage media, and patterns (by lithography or the like): to be specific, the production of high-density magnetic recording media, nanowires, quantum dots, metal dots or the like.